The invention relates to a technology of updating location information for setting up a call between communication terminals.
Over the recent years, so-called IP phones have spread, wherein a call is set up between communication terminals via an IP network such as the Internet, and the communication terminals converse with each other by transmitting and receiving voice packets based on Internet Protocol (IP).
In an IP telephony system, the communication terminal sends a Register message (REGISTER) defined as a location registration request to a Registrar as one of components of an SIP (Session Initiation Protocol) server that performs call control, and the Registrar accepts the request and registers the location information such as an IP address of the terminal in a subscriber information DB of the SIP server. The SIP server executes a call process such as transmitting and receiving a call on the basis of the information registered in the subscriber information DB.
Further, for instance, a technology disclosed in the following Patent document 1 is given by way of the prior art related to the invention of the present application.
[Patent document 1] Japanese Patent Application Laid-Open Publication No. 2004-274602